.NET/ASP.NET/C#/VB.NET PDF Document SDK

Generating dynamic HTML has always been difficult. As we ve discussed, in the early days of the Web, you had CGI and then servlets. Of course, both of these solutions worked, but at their core, they created HTML content via string concatenation. As any servlet developer will tell you, string concatenation is difficult to develop, tedious, error prone, and hard to maintain. Template models such as JSP and ASP were created to ease the burden by allowing you to use normal HTML with some special markup to develop dynamic pages. These pages are much easier to build and maintain than their string concatenation cousins. As you ve seen in some of our examples, using Ajax to generate dynamic content creates many of the same issues you can use DOM methods to create content, but this approach can be irksome and often results in lots of extra code. Since you re reading this book, you re better equipped than the average developer; however, trust us when we say some DOM methods behave differently across browsers. Many people have come to rely on innerHTML combined with string concatenation when they decide to put a new Ajax feature in their application. Although building the innerHTML content on the server (taking advantage of your favorite language) certainly helps, it still doesn t negate the issues with innerHTML. Though widely supported, innerHTML is not a W3C standard. You can do a lot with innerHTML, but it has its limits. For instance, you can t insert a table row between other table rows. Of course, the biggest challenge, and we re sure this will come as a shock to many of you, is that innerHTML behavior varies across browsers.

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This example may have seemed trivial, but you can actually go quite a long way with this technique. The next example takes things to their natural conclusion, actually drawing the shapes on a form: #light open System open System.Drawing open System.Windows.Forms

Inexpensive digital cameras or web cams make great attachments for making remotely guided vehicles. It s as if you re riding along as you pilot your vehicle while watching the live video on the computer screen. The cameras are easily mounted to the Quick Start Vehicle with a just few beams, as shown in Figure 14-32. You ll probably want to buy some USB extension cords to expand the area you can explore, but USB can t be extended much beyond 16 feet (5m) total. If you used Bluetooth for control and a wireless camera, your vehicle would be completely untethered.

Taconite solves this core issue by providing a custom parser that converts HTML into the equivalent W3C DOM methods used to create the specified content. This means you can write dynamic content using whatever HTML-generating technology with which you re most comfortable. You get the best of both worlds: you get your snazzy new Ajax feature without dealing with string concatenation or using standard W3C DOM calls. And since we re such nice guys, we ve taken care of all the nasty cross-browser issues! This parser is used by a set of custom JSP tags that allow you to write content in a way that is natural as HTML embedded within a JSP You no longer have to crowd your pages with a . slew of document.createElement and document.appendChild commands to dynamically create new content. The JSP custom tags working with the parser take care of all this while you sit back and enjoy your refreshing iced mocha! The resulting JavaScript is returned to the browser as part of the response where the client-side JavaScript library takes over and executes these commands to produce the desired output. Taconite doesn t try to reinvent the wheel; instead, it focuses on the Achilles heel of Ajax development: the potentially tedious task of writing large amounts of JavaScript to dynamically update your Web page. Unlike some toolkits, Taconite doesn t try to invent a new way of sending request data to the server; instead, it relies on the tried-and-true name/value pairs either embedded within the query string of a GET request or tucked safely in the body of a POST. The client-side library even automates the creation of the name/value query string heck, we